The modern HUD was bred, like many inventions, as an instrument of war.

Arguably the first HUD device was the reflector sight, invented in 1900 by Sir Howard Grubb, an Irish optics designer. As the site incorporated optics to focus on targets at a distance and employed optical tricks to paint a cross hair on the image, the human eye was able to focus on the cross hair and target at the same time -- a major advance in targeting.

Previously marksmen using crossbows or guns relied upon metal fore-sight and back-sight target devices, composed of solid crosshair members. These devices came into use in medieval times, with the original inventor(s) unknown. The problem was that the eye could only focus on one distance at a time; hence it was in focus with the target and out of focus with the crosshairs -- or in focus with one of the crosshairs, but out of focus with the target.

Despite Sir Grubb's invention, for the next few decades most guns continued to use traditional sights, some of which did have novel twists such as the use of black widow spider silk.

II. Boom! The HUD Explodes on the WWII Battlefield

The reflector sight was reserved for one area in which performance trumped price -- aircraft combat. Germany was the first to use the sight in its biplanes in World War I (WWI) in 1918. During WWII HUD-type sights proved especially critical in nighttime raids and in battles in inclement weather.

In the following years the first interactive heads up display -- a gyro-corrected gunsight -- was developed in 1935 by the Carl Zeiss and Askania Werke companies for the Nazi's Luftwaffe. The more accurate sights gave German pilots a significant edge during the WWII Battle of Britain waged over the skies of London in summer and autumn of 1940. (Today Carl Zeiss makes some nifty lens for our camera smartphones and Askania makes luxury watches.)

HUDs gave the Nazis a key advantage in the Battle of Britain. [Image Source: Barry Weekley]

Ironically another high-tech invention by Germany -- radar -- combined with the homefield advantage of being able to return downed pilots to action allowed the British to overcome. Radar waves had been discovered in 1886 by famed German researcher Heinrich Hertz and had been used in detection by German inventor Christian Hülsmeyer in 1904, but by WWII the British had the superior implementation of the technology. Hence the Royal Air Force (RAF) could see in advance German aerial units massing for attacks, a crucial factor that allowed them to disrupt the bombings.

The British Royal Aircraft Establishment's (RAE) Farnborough airfield had an active research unit, which in 1941 developed a comparable device for allied aircraft, possibly inspired by parts from downed German fighters. While not as accurate as the German sights, it would go on to inspire the victors of the merits of HUDs.

III. Computer HUDs -- Post-War Progress

The Allies also developed the first electrical HUD -- a projected image of radar onto the windshield of British AI Mk VIII fighters used in night raids. That success inspired the U.S. Navy's Office of Naval Research and Development (ONRD) to in the post-ward days devise a concept of a project information display containing flight speed, trajectory and other useful info. Published in 1955, that concept perhaps inspired The Rank Group, a UK movie company, to utilize its Cintel group to develop a production version.

In 1958 Cintel won a contract battle with supporters of the old electromechanical sights. While those critics billed the Strike Sight as risky, foolhardy solution, its success would set a new standard for aircraft, pushing HUDs into widespread daytime use, first in the late 50s and 60s Cold War era air forces, and by the 70s in the commercial aircraft sector.

The Buccaneer would go on to blaze more new ground, becoming perhaps the first HUD to use printed circuit boards.

IV. HUDs Accidental Journey Begins With a Death

The first automotive HUD was, in essence, inherited from the WWII in more ways than one. Howard Hughes, an American actor who had rose to prominence first as a pilot then as a WWII aircraft designer, died in 1976, leaving behind a $2.5B USD estate, two ex-wives and decades of controversy over an allegedly forged will.

Howard Hughes, sketched by an artist, is depicted here held by a bodyguard near the time of his death in 1976. [Image Source: TIME]

His treasured aircraft company would eventually go on the auction block to fund the Howard Hughes Medical Institute (HHMI). In the mid-1980s aerospace was a booming market and this was a rare opportunity. Many companies showed an interest in bidding.

General Motors Comp. (GM) charged, or by some estimations stumbled, into the role of HUD pioneer when it purchased Hughes Aircraft in 1985. The acquisition was primarily aimed at capturing the prized Delco Electronics unit, which made car radios, but GM would look to other ways to profit on the investment. It directed the Hughes Aviation and Delco units to work together to ready the HUD and other useful technologies for automotive use. Together, the two units produced the world's first mass-market HUD, which GM offered as an option for the 1988 Oldsmobile Cutlass Supreme.

The onboard HUD would display speed and turn indicators.

[Image Source: Popular Mechanics]

Over the following few years other lower volume luxury vehicles would also adopt the technology, which at the time relied on incandescent lamps to project the displayed image. Newer early-90s Oldsmobile models would continue to use the technology in low quantities, while largely ditching the eye-catching digital gauges of the 1988 model.

Here's a video of a 1992 Oldsmobile Cutlass Supreme's HUD during highway travel.

The HUD was officially on the road.

V. The HUD Quietly Matures

Competitors to GM's in-house design team soon arose. Among them was Japanese parts firm Denso Corp. (TYO:6902), who produced its first HUD in 1991. That same year the movie Knight Rider 2000 showed off an even more ambitious HUD concept. The new version (the Knight 4000) of everyone's favorite talking car, KITT featured a sleek HUD that could use much of the windshield to display info.

Early designs suffered from a phenomenon known as "ghosting", which made a double image of the HUD appear. A solution came in the 90s thanks to an interlayer technology from E. I. Du Pont De Nemours And Comp. (DD). Commented Scott Spink -- an optical engineer at the then-largest supplier of in-car HUDs, Delphi Delco -- back in 2001:

In the Heads-Up Displays, the image that the driver sees is reflected off the inner and outer surfaces of the windshield. The inner surface produces the primary image seen from the driver's position while the outer surface produces a second, dimmer image. In a conventional, non-wedged windshield, these images appear slightly separated due to refraction through the glass layers and this separation is known as 'ghost'. Thanks to wedged PVB, we can align the two images into one, eliminating 'ghosting'. DuPont supplies the wedged PVB for our most popular HUD systems.

Most automotive HUDs rely on projection. [Image Source: Laser World]

GM was a top customer. In the same interview, Delphi Delco's EyeCue Product Manager, Dale Hopkins, commented on the polyvinyl butyral (PVB) resin wedge technology:

One of our biggest customers is General Motors which offers HUDs in its major option package for the Pontiac Bonneville, Grand Prix and Buick Park Avenue models. We also recently won a GM contract for HUDs in Pontiac's 2001 minivan model and for Chevrolet and Buick 2002 models.

Whereas current commercializations use a fixed segment HUD, displaying basic data such as the speedometer reading, fuel and temperature levels, the new minivan commercializations will have reconfigurable HUDs. This means that they will be able to display a wider range of alphanumeric information concerning cellphone, radio and turn-by-turn navigation information, as well as other data currently displayed on the driver's dashboard information center. As an example, information from Japan's 'intelligent highway systems' could be displayed well on our reconfigurable HUD's.

Wedged PVB provides the best cost-performance choice for today's automotive manufacturers when it comes to HUD technology. We had considered alternative technologies such as holographic patches for Delphi's HUDs but these were simply too costly for mass commercialization. Butacite® wedged PVB does the job perfectly.

DuPont's Butacite reduced ghosting, a common problem in projected HUDs.

Prices have continued to fall. Back in 2001 HUDs cost around $1,000 USD as an option. GM was by far the biggest adopter with many Pontiac, Cadillac, and Buick models, plus the Corvette having the tech. Bayerische Motoren Werke AG (ETR:BMW) was another major adopter, with HUD options in its 5 and 6 Series models.

The BMW 3 Series now has a HUD that displays the speed limit, which it spots on signs, plus your current speed.

When GM's patent exclusivity on HUD technology expired in 2005, some expected HUDs to quickly permeate most mass market vehicle brands. But progress has been slow, gradually building momentum, largely on the luxury end,

In 2012 the HUD market was estimated by MarketsAndMarkets to be a $991.86M USD business, only about a twentieth of a single percent of the auto industry's total yearly sales, which total around $2T USD [source]. Of the 81.8 million vehicles sold in 2012 globally [source], less than one in a hundred (800,000 total) had a HUD [source]. Estimates from 2013 generally indicate substantial pickup in HUD-equipped models, but IHS Automotive estimates that they still comprise less than 2 percent of total vehicles sold last year.

The new HUD tech from MIT could help change that.

It uses a familiar friend -- the nanoparticle -- to remedy the shortcomings of its predecessors.

Silver nanoparticles, like those pictured here, are used in the new HUD tint. [Image Source: Future Chemistry]

Laser projectors are bright, but are overly expensive. LED backlit projectors are cheaper, but often suffer somewhat in image quality, even with interlayers' such as the DuPont's Butacite.

The MIT tech -- developed by the labs of MIT physicsprofessor Marin Soljacic and John Joannopoulos -- looks to remedy the flaws of each approach. Graduate student Chia Wei Hsu worked with his advisors to devise the new approach, which is essentially a nanoparticle thinfilm that can be "painted" on existing windshields.

Graduate student Chia Wei Hsu is pictured second to the end on the left, along with advisors, MIT physics professors John Joannopoulos (center) and Marin Soljacic (to the right of center).
[Image Source: MIT]

The demo system consisted of a thin layer of silver nanoparticles. The blend used contained nanoparticles that were approximately 60 nm in diameter.

[Image Source: MIT/Nature Comm.]

The key to the new technology is the extreme specificity and high light absorbance rates of nanoparticles at specific wavelengths of light. The silver particles respond to blue light, producing a brilliant, sharp image.

The nanoparticles can be tuned to be very close to the desired theoretical performance.
[Image Source: MIT/Nature Comm.]

The nanoparticles can contain various metalloid cores, such as silicon, which alter their light absorbing and scatter properties.

The system could allow cheap LED-projected images to produce in-car HUD images with brightness and crispness that rivals laser-projected designs, although it will require tuning the nanoparticle to the LED's wavelength or picking an LED that emits on a wavelength the nanoparticle is receptive to. Alternatively, you could use the coating to improve the results of traditional laser projectors, eliminating ghosting and other artifacts of projected images that rely on internal windshield glass reflection.

(A reader SAString points out that GM actually worked on a similar display concept, albeit with lower contrast. They also point out that focusing the image on the field of vision is difficult with these kinds of active glass technologies.)

The solution is optimal from a visibility perspective. Professor Soljacic explains, "The glass will look almost perfectly transparent because most light is not of that precise wavelength. [Silver nanoparticles were used because it was] something we could do very simply and cheaply. [The unoptimized result] gives us encouragement that you could make this work better."

[Image Source: MIT/Nature Comm.]

Aside from automotive and aviation displays -- the most widespread current commercial HUD uses -- the technology could prove crucial to emerging HUD applications, as well. Such examples include wearable electronics and transparent window displays. An MIT release summarizes:

The particles could be incorporated in a thin, inexpensive plastic coating applied to the glass, much as tinting is applied to car windows. This would work with commercially available laser projectors or conventional projectors that produce the specified color.

Such displays might be used, for example, to project images onto store windows while still allowing passersby to see clearly the merchandise on display inside, or to provide heads-up windshield displays for drivers or pilots, regardless of viewing angle.

To create a finished version of the HUD, the MIT team will likely look to hunt down inexpensive red and green nanoparticles to complement its current blue coat. Together these three coats could allow a combined windshield or window paint that acts as a very narrow filter, displaying a projector's intended image with brilliant precision, but also allowing natural light to pass through without inadvertently illuminating the thin film.

The aforementioned MarketsAndMarkets report estimated that by 2017, the HUD market will triple to $2.91B USD by 2017. But if the MIT researchers can complete their quest to enable the ultimate HUD display, that estimate could prove conservative. It could drive a more ambitious target set by IHS Automotive -- a division of analyst group IHS Inc. (IHS) -- which has stated that it expects 9 million HUD-equipped consumer vehicles (roughly 9 percent of the market) to be sold by 2020.

The work was partially funded by the National Science Foundation (NSF). Given the ongoing use of HUDs in aerial combat and the emerging need for HUDs in ground combat vehicles, it is not surprising that the research is also funded by the Army Research Office (ARO) (Grant no. DAAD-19-02-D0002).

Future soldiers will likely look to field the tech in combat vehicles, as well.
[Image Source: RDECOM PAO]

While HUD tech has radically evolved since the simple reflector sight, it still remains closely tied to its combat roots. Mankind for centuries has looked to augment his reality; perhaps no device is more symbolic of that quest than the HUD. Today we live in an exciting era in which we may at last augment our vision with information to sell products or make our daily drive a bit easier. But as compelling as such uses may be, they remain to some extent a novelty.